Each year hundreds of thousands of people are afflicted with vascular diseases, such as arteriosclerosis, that result in cardiac ischemia. For more than thirty years, such disease, especially of the coronary arteries, has been treated using open surgical procedures, such as coronary artery bypass grafting. During such bypass grafting procedures, a sternotomy is performed to gain access to the pericardial sac, the patient is put on cardiopulmonary bypass, and the heart is stopped using a cardioplegia solution.
More recently, techniques are being developed, for example, by Heartport, Inc., Redwood City, Calif., that permit cardiac surgery using an endoscopic approach, in which small access openings are created between the ribs and the bypass graft or heart valve repair procedure is performed guided by an image displayed on a video monitor. In the "keyhole" techniques developed by Heartport, the patient's heart is stopped and the patient is placed on cardiopulmonary bypass. Still other techniques being developed, for example, by CardioThoracic Systems, Inc., of Cupertino, Calif., enable such bypass graft procedures to be performed on a beating heart.
In those techniques that involve stopping the heart to perform the surgery, blood flow to the heart is occluded, for example, by placing occlusion balloons in the ascending aorta and/or the vena cava. Venous blood is then withdrawn from the patient, for example, from the vena cava, and oxygenated using an extracorporeal oxygenation circuit. The oxygenated blood is then perfused into the patient in the vicinity of the ascending aorta to provide oxygenated blood to the brain, internal organs and extremities.
U.S. Pat. No. 5,312,344 to Grinfeld et al. describes a multi-lumen perfusion catheter for perfusing oxygenated blood into a patient on cardiopulmonary bypass. The catheter has a distal balloon for occluding the ascending aorta, a first lumen for delivering cardioplegia solution through a first opening distal to the balloon, and a second lumen for perfusing oxygenated blood through a second opening proximal to the balloon. The catheter may be positioned in the ascending aorta either directly through an opening in the aorta, or in a retrograde manner via a femoral artery and the abdominal aorta.
U.S. Pat. No. 4,173,981 to Mortensen describes an arterial perfusion catheter having a tapered shape and a plurality of openings along its length. When the catheter is positioned within a patient, one or more openings preferably are aligned with the branch vessels in the aortic arch, the renal arteries, the iliac bifurcation, and the internal iliac artery.
The foregoing catheters have a number of disadvantages. In particular, multi-lumen catheters, such as described in Grinfeld et al., must have a large diameter to provide oxygenated blood sufficient to perfuse the whole body. In addition, because the foregoing catheters preferably are positioned with the blood perfusion openings in predetermined locations, a variety of catheters of different lengths must be available for use in patients of different sizes.
The perfusion system described in the literature by Heartport, Inc., Redwood City, Calif., comprises an "endo-aortic clamp" ("EAC") portion and an arterial return catheter ("ARC"). The EAC, which comprises a catheter having a balloon for occluding the aortic root, and a lumen for delivering cardioplegia distal to the balloon, passes through the ARC. The ARC extends only a short distance into the patient's femoral artery. Oxygenated blood is perfused through the annulus formed by the ARC and the EAC and in a retrograde manner in the aorta.
A drawback associated with all of the foregoing perfusion systems is that all require relatively high performance pumps to deliver flow rates high enough to perfuse the entire body. In multi-lumen catheter designs, the pressure drop encountered in delivering a high flow rate proximal to the occlusion balloon favors the use of larger diameter lumens, thereby resulting in catheters having a profile too large to fit many patients having smaller frames or vessels.
Similarly, in the Heartport system, the need to perfuse the blood in a retrograde fashion along the length of the aorta requires a high performance pump. This is especially so because the oxygenated blood is perfused into the iliac artery, where the degree of oxygenation is relatively low, and must then flow in a retrograde manner through the aorta to reach the aortic arch, where the highest flow rates are required to preserve the brain.
In view of the foregoing, it would be desirable to provide apparatus and methods for delivering oxygenated blood to a patient from a cardiopulmonary bypass machine, and that overcome the drawbacks of previously known perfusion catheters.
It further would be desirable to provide apparatus and methods for delivering oxygenated blood to a patient that permit the use of one or more lower performance pumps than has heretofore been possible.
It still further would be desirable to provide apparatus and methods for delivering flow rates to different regions of the body in proportion to the degree of oxygenation required by those different regions.